Canulated titanium implant for correcting flat feet in children

ABSTRACT

It is possible to satisfy all the requirements of minimal invasiveness with maximal permanent result by placing the invented implants (screw). The shape of the screw solves all mentioned technical problems that occurred thus far, i.e. it can be directed through a small gap in the skin by Kirschner&#39;s guide-wire (because the screw is hollow-canulated). The screw is larger in body, so a much greater force is needed for it to break. If it does break, it can be removed easier with less lesions to the surrounding bone tissue. At the point of the screw are trisect cuts (on the apex thread) which also make the lesion of the bone lesser as is as it is inserted in its position. Since the head of the screw is bigger and conical, without a narrow part leading to the screw-thread, the screw self-tightens into the bone, which makes the loosening rarer. The loosening is also rarer because of the shape of the screw-thread. The screw has the equal effect throughout the whole time it is implanted in the body. The osteolysis of the heel bone in which the screw stems against is also reduced. The conical shape of the head of the screw, without a narrow part (neck) between the head and the screw-thread, it does not allow ingrowing of the bone tissue, so it can be easily removed when the necessary time of correction is finished. The time necessary for the surgical procedure is significantly shorter, taking up 15 minutes, thus reducing the possibility of a infection, which is also helped by a small operative area. After the placement of the screw, the patient can walk two days after the surgery and he/she does not need any plaster immobilization or physical therapy. The screw is made out of titanium alloy, which gives it a certain toughness; the patient can undergo magnetic examinations, if there is need for such, while the screw is implanted.

DESCRIPTION OF THE INVENTION

1. Field of the Invention

This invention was designed for the operative correction of extremelyflat feet in children with a heel valgus (Pes planovalgus gr III-IV),which in spite of using all existing physical methods of correction andusage of orthrotics by the age of twelve could not correct the axis ofthe heel and bring the arch of the heel to a permanent satisfyingresult.

2. Technical Problem

There have been many years now that one has tried to solve the problemby different surgical methods, but they have up to now demandedoperative opening of tarsal bones (by an incision of 30-50 mm), i.e. byopening the operative area to change the relation of tarsal bones (thefoot bones), the surrounding tissue needed to be lesioned.

The screw could have been directed in the right position and into theright place by opening the surface of the bone. Therefore, thepost-operative recuperation took longer, and in many cases a long-term(several weeks) mobilization was needed.

The second problem was that of the breakage of the inserted screwsbefore the correction of the feet was completed. Removing the remainingbits of the screw resulted in damaging a great deal of the healthy bone.

The third problem was the premature loosening of the screw, which shouldhave worked for 30 months (the screws were implanted during that periodof time) so that the proper correction of the arch of the foot and theaxis of the heel would take place as the feet develop.

The fourth problem was the existing ordinary head of the screw. Whenremoving it per cutem, one needed to use the injection needle to locatethe head of the screw for it to be drilled out, which was harder to do.Again, one had to operatively remove the screw, since the head of thescrew was in the shape of the ball, which rested on a thin neck, thehead of the screw could catch the edge of the heel bone, whichdefinitely was of no advantage.

The fifth problem occurred with the resorptive screw (if such wasimplanted—so italian authors), which broke already after six months ofits placement, so the long-term correction process of thirty months thatis needed, comes into question. According to the anglo-saxon authors,this implant is unstable and falls out before the required period ofcorrection is finished. We also do know sufficiently enough of how thematerial affects the body, it falls apart and is resorbed during thetime it was implanted. This invented screw solves all these problems byits shape and construction, i.e. it can be inserted through a small skingap directed by Kirschners's guide-wire (it is canulated). The screw'sstem/body is much stronger and larger, therefore, a much bigger force isneeded for the screw to break, and even if it does break, it can beremoved easier with a much lesser lesion of the surrounding tissue. Thepoint of the screw has apex thread, which also lessens the lesion of thebone while positioning it. Since the head of the screw is bigger andconical by its shape, and the screw does not have a thin neck. Thescrew, as it is positioned, sets into the bone by self-tightening intoit. Therefore, it rarely loosens. The screw cannot grow into the bonetissue because it has a conical head and no thin neck between the headof the screw and the screw-thread, so it is easier to remove it when thecorrection process is finished.

The screw is made out of titanium alloy, which gives it a particularstrength, and the patient can undergo magnetic examinations, if there isany need for such while the screw is implanted.

3. State of the Art

The techniques of the surgical method “Calcaneo stop” used thus far forcorrecting flat feet, used different screws which were placed into thealready mentioned feet bone in anterograde (talus) and retrograde(calcaneus) direction. The resorptive screw, which is placed in thesinus, i.e. in the gap between the mentioned bones.

While placing the already known screws one had to show the sinus, i.e.operative area to display the bones in which one would place the screwsin the correct position. So far, the used screws were as follows:

-   -   The ordinari spongious screw, which is placed in talus        anterograde, breaks transversally in 5-10% of patients. Placing        of the screw is not sufficiently correct if one does not open        the operative area. Bad direction of the screw while positioning        and placing it, happens in 4-9% of patients according to our and        the analysis from the rest of the world. The head of the screw        is round, so it sinks into the heel bone during the correction        process and the effect of the correction of the axis of the heel        bone (calcaneus) becomes over time smaller.    -   The Casteman screw is also placed anterograde in the talus bone.        The positioning, i.e. placing of the screw precisely is        questionable (there is no directing of the screw), the same as        in the ordinary spongious screw. The authors mention its        premature loosening in 5-7% of patients. The screw's neck is        conical and narrower than the screw-thread, so there is no        effect of self-tightening, so the bone mass can grow into it,        which could cause a problem when removing it.    -   The resorptive Giannini screw which is placed in the sinus, i.e.        in the gap between the heel bone and the talus bone, so it        breaks regularly already after a year of its placement and        slowly desintegrates, so the quality of the correction comes        into question (it does not support the foot long enough in the        corrective position), and we do not know sufficiently enough        about the affects of the resorbed material. Some authors point        out its premature loosening and falling out of the positioned        place, so they do not recommend it.    -   The retrograde Nogarin screw, which is placed in the heel bone        (calcaneus) retrograde, is also carried out by largely opening        an operative area. The authors point out loosening of the screw        in 5% of patients, and penetration of the same into the talus by        6% of the patients. This screw does not have a head, but a neck,        which is narrower than the screw-thread, so the self-tightening        cannot be achieved, therefore it penetrates into the talus bone        easier.

THE ESSENCE OF THE INVENTION

The invented screw (implant) achieves complete correction (immediately)after the surgery. It is only necessary to make an incision into theskin of 8 mm (equal to the diameter of the implant). The screw isdirected through the incision, while the other tissue is simply pushedaside and not cut (like e.g. ligaments) so the screw could be positionedinto its temporary place (the foot bone). It is not necessary anymore tooperatively open an area of 30-50 mm, i.e. harming the surroundingtissue. Because of its canulated shape, the invented implant can beeasier correctly placed through a small gap in the skin (in a 3-Ddisplay) using the Kirschner's guide-wire while checking it with thefluorograph, not harming the cartilage nor the talus bone, if it isnecessary to do several attempts to position the screw (implant)correctly.

The point of the screw has an apex thread which reduces the damage ofthe bone tissue. It allows the implant to go through easier, as well asthe positioning in the bone.

The body of the screw implanted is larger so it is more resistible totransverse breakage. If the implanted screw does break in time, it ismuch easier to remove it because of its canulated shape. The type of thescrew-thread, whose edges are wider and lean at the angle of 45°±25%reduce the loosening of the screw, which makes greater contact to thesurface to the spongious bone, therefore a greater stability of thescrew to transverse force.

The shape of the head of the screw is conical. The spongiousscrew-thread continues into the conical head which is smooth to the topof the head of the screw. That makes the free movement of the calcaneusbone in regard to the talus bone while walking—i.e. the calcaneus bonedoes not catch at the head of the screw but it directs the bonegradually in the correct movement, i.e. position. The screw does nothave a thin neck (the screws with the thin neck proved to break in 5-10%of patient) is much stronger. The conical head which leads to thescrew-thread makes the self-tightening into the spongious bone possibleand stops the premature loosening of the screw.

The conical head does not allow the screw-thread to grow into thecortical (strong) bone, so there are no problems when the implant/screwneeds to be removed. The conical head allows a permanent pressure on theheel bone (during the period of the correction), not catching at thebone tissue (like other screws), therefore the implant does not make animprint on the heel bone, i.e. it does not penetrate into the bone. Thisscrew has the equal effect throughout the whole period of correction,i.e. three years. It is made out of titanium alloy, which is tougher, soit stops breakage of the screw in the area of insertion into the bone.It allows MR (magnetic resonance) examinations if there is need for oneif another illness appears.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the procedure of placing the screw into the talus bone. Itshows in which bone the screw is inserted, at which angle it is placedusing the Kirschner's guide-wire and canulated imbus.

FIG. 2 shows the screw itself—technique data. There is a conical head ofthe screw and its screw—thread with the apex thread on the point. Thewhole screw is canulated, so it can be easier directed.

FIG. 3 shows the screw and the instruments (Kirschner's guide-wire andthe imbus), which are used in the operative procedure as the screw isplaced in the foot bone.

FIG. 4 shows the screw from its front and rear view.

DETAILED DESCRIPTION OF THE INVENTION EMBODIMENT

The placement of the screw and the procedure of insertion is clear fromthe previous pictures, as well as the instruments used for placing thescrew. The screw is being used in treatment of painfully activecorrectable flat feet (3-4^(th) stage) in children of the age 8-12years, without plegia of the nervous system.

The screw is inserted as the patient undergoes general endotrachealanesthesia and removed under local anesthesia. After the pre-operativefeet cleaning, a surgical incision of 8 mm is made into the skin. A bandof fibrious tissue (fascia) is moved aside as well as the ligamentslengthwise using small surgical scissors. The insertion position and thedirection of the screw (implant) into the talus bone is determined byusing the drill and Kirscner's guide-wire, 1.8 mm in diameter, whosepositioning is controlled by the fluorograph, which identifies theinsertion place and the direction firstly of the guide-wire and then thescrew into the talus bone, anterograde by 35° on the sagittal centerlineplane and 45° on the frontal plane of the body. The length of the screwis determined by the other guide-wire, which is of the same length ofthe first guide-wire; then using the canulated drill, 4.5 mm thick, onemakes an opening in the cortical bone then, one places the screw on theguide-wire and so using the canulated imbus spanner drills into thetalus bone.

One checks the mobility of the foot ankle and correction of the axis ofthe heel bone as well as the correction of the longitudinal arch of thefoot. After that, one drills out the Kirschner's guide-wire. Theligaments are repositioned, the band of the fibrious tissue (fascia) andthe skin are closed each by one stitch.

The patient can get up two days after the surgical procedure and walk,without using any immobilisation.

The screw stays implanted in the foot up to 30 months, depending on theage of the patient when the implant is first inserted.

It is removed, as one wishes, using local anesthesia. Meanwhile, thepatient can take up sports without any obstacles.

There are 4 lengths of the screw, which is made out of titanium alloy,which is placed depending on the need, i.e. the size of the feet bones,therefore the length L (FIG. 2) is recommended:

-   -   25 mm±25%, recommended 25 mm±10%, and especially recommended 25        mm,    -   30 mm±25%, recommended 30 mm±10%, and especially recommended 30        mm,    -   35 mm±25%, recommended 35 mm±10%, and especially recommended 35        mm,    -   40 mm±25%, recommended 40 mm±10%, and especially recommended 40        mm,

With the change of the length of the screw L, the length of the head ofthe screw H is being proportionally changed (FIG. 2):

-   -   10 mm±25%, recommended 10 mm±10%, and especially recommended 10        mm,    -   12 mm±25%, recommended 12 mm±10%, and especially recommended 12        mm,    -   14 mm±25%, recommended 14 mm±10%, and especially recommended 14        mm,    -   16 mm±25%, recommended 16 mm±10%, and especially recommended 16        mm,

The implant (screw), independently from the length L, canulated by thetunnel (FIG. 2) of the diameter C=2 mm±25%, recommended 2 mm±10% andespecially recommended 2 mm.

The diameter of the screw stem D (FIG. 2) is 4.8 mm±25%, recommended4.8±10%, and especially recommended 4.8 mm.

The outer diameter of the screw-thread E (FIG. 2) is 7.1 mm±25%,recommended 7.1 mm±10%, and especially recommended 7.1 mm.

The part of the screw with the screw-thread continues directly into theconical head (without the narrow neck) between the head and thescrew-thread.

The maximal diameter of the conical head A (FIG. 2) is 8 mm±25%,recommended is 8 mm±10%, and especially recommended 8 mm.

The conical shape of the head allows self-tightening into the bone inwhich the screw is inserted, which gives the screw stability as it isinserted. Therefore, the loosening as well as the breakage of the screwis minimal.

The conical part between the head that leads into the stem allowsstemming against the bone on the larger surface of the screw, i.e. thereis no osteolysis of the bone structure of the heel bone on the pressurepoint of the screw (because the pressure is lessened), so the correctionis permanent and has the equal effect during the period of the screw isimplanted.

The screw that has the step-like part between the head of the screw andthe stem, has proven to catch at the edge of the heel bone and thereforerestrict the movement.

The invented screw does not restrict the movement from the moment it isplaced and there on. The recess of the hexagonal hole in the screw head(FIG. 2) for the imbus spanner is B=4.5 mm, and makes 4.5 mm±25%,recommended 4.5 mm±10%, especially recommended is 4.5 mm.

The screw-thread has the usual ascent for the spongious bone by 2.7 mm(FIG. 2). Its edges are thickened (FIG. 2). The edges of thescrew-thread finish at the angle Q=45°±25%, recommended 45°±10%, andespecially recommended is 45°. This angle allows the thread edges tolean on the spongious bone with grater surface, i.e. at the samediameter of the screw, a greater contact surfaces is achieved betweenthe bone and the implant (screw), which allows greater stability to thetransverse force, and therefore a lesser possibility of loosening. Onthe point of the screw, which ends at the angle of 90°, on the apexthread there are trisect cuts at the angle of 120°. The edges of theapex thread are cut at the angle of 55°. At the very top of the point ofthe screw, the trisect cuts of the apex thread go inward the tunnel inthe length of the screw by 1.5 mm.

The invented implant (screw) is characterized by a simple-minimallyinvasive way of placement. Using the Kirschner's guide-wire of adiameter 1.8 mm, the screw's direction and the length is determined (35°on the sagittal centerline plane and 45° on the frontal planeanterograde). It is then inserted into the talus bone with the imbusspanner. There are trisect cuts on the apex thread, which automaticallyexclude the usage of tapping device.

Since there is no narrow part (neck) between head and the screw-thread,the cortical bone does not arrest the screw. This makes removing of thescrew after 3 years of correction easier and more simple.

THE USAGE OF THE INVENTION

The invented implant-screw makes the surgical procedure more simple andminimal invasive for the body and surrounding tissue. The post-operativeduration is shortened as much as possible. The correction of the feet iscomplete and permanent.

Complications that arise, e.g. because of the bad positioning, looseningand/or breakage of the screw are minimal when compared to the alreadyknown methods and screws (implants). It allows a much higher percentageof satisfying post-operative results.

The possibility of post-operative infections are lesser as well, becausethe operative area is reduced. The patients can be examined by MR, whilethe screw is implanted, if such examination is necessary, because thescrew is made out of titanium alloy. With other alloys this examinationis forbidden.

1. The canulated titanium implant (screw) for correction of flat feet inchildren characterized by that: a) the diameter of the stem is D=4.8mm±25%, recommended 4.8 mm±10%, and especially recommended 4.8 mm, b) itis canulated, whose diameter is C=2 mm±25%, recommended 2 mm±10%, andespecially recommended 2 mm, c) the screw-thread height is 1.15 mm±25%,recommended 1.15±10%, and especially recommended 1.15 mm, d) on thepoint of the screw, which ends at the angle of 90°, on the apex threadare trisect cuts at the angle of 120°. The edges of the apex thread arecut at the angle of 55°. At the very top of the point of the screw, thetrisect cuts of the apex thread go inward the tunnel in the length ofthe screw by 1.5 mm, e) this type of the point replaces the use of thedrill and the tapping device.
 2. The implant according to the invention,according to claim 1, characterized by that: a) the screw-thread is ofthe usual ascent for the spongious bone for 2.75 mm, whose edges arethickened, b) the screw-thread edges end at the angle of Q=45°±25%,recommended 45°±10%, and especially recommended 45°. The screw-threadleans on the spongious bone with grater surfaces, i.e. at the samediameter of the screw a greater contact surface is achieved between thebone and the screw, which allows better stability to the transverseforce, therefore a smaller possibility of loosening.
 3. The implantaccording to the invention, according to claim 2, characterized by thefact that: a) the outer diameter of the screw-thread E is 7.1 mm±25%,recommended is 7.1 mm±10%, and especially recommended 7.1 mm, b) thepart of the screw with the screw-thread directly continues into a smoothconical head (with no narrow neck), c) the maximal diameter of theconical head of the screw A is 8 mm±25%, recommended is 8 mm±10%, andespecially recommended 8 mm, d) hexagonal recess in the head, for theimbus spanner with the dimensions B=4.5 mm, recess dimensions F=4.5mm±25%, recommended 4.5 mm±10%, and especially recommended 4.5 mm. 4.The implant according to the invention, according to claim 3, ischaracterized by: a) the length L, which is 25 mm±25%, recommended 25mm±10%, especially recommended 25 mm, 30 mm±25%, recommended 30 mm±10%,especially recommended 30 mm, 35 mm±25%, recommended 35 mm±10%,especially recommended 35 mm, 40 mm±25%, recommended 40 mm±10%,especially recommended 40 mm. b) the length of the conical head of thescrew H is 10 mm±25%, recommended 10 mm±10%, especially recommended 10mm, 12 mm±25%, recommended 12 mm±10%, especially recommended 12 mm, 14mm±25%, recommended 14 mm±10%, especially recommended 14 mm, 16 mm±25%,recommended 16 mm±10%, especially recommended 16 mm, c) the screw ismade out of titanium alloy.
 5. The implant according to the invention,according to claim 4, characterized by that: a) the screw-thread,without the narrow part continues into the conical head which is widens,b) the conical shape of the head allows self-tightening into the bonewhere the screw is inserted in, that makes the position of the screwmore stabile, therefore makes the breakage and loosening of the screwminimal.
 6. The implant according to the invention, according to claim5, characterized by the fact that it is conical in shape and notstep-like, so the part between the head and the screw-thread allows thescrew to stem against the heel bone on the greater surface of the screw,i.e. there is no osteolisys of the heel bone structure in the pressurepoint (because pressure is lessened) of the screw, so the correction ispermanent and equally has an effect during which time the screw isimplanted.
 7. The implant according to the invention, according to claim6, characterized by the fact that there is no step-like part between thehead of the screw and the screw-thread, which can catch at the edge ofthe heel bone, and therefore the movements are entirelyfree/unrestricted from the moment of the screw's placement and there on.8. The implant according to the invention, according to claim 7,characterised by that: a) the procedure of its placement, which is verysimple-minimally invasive to the body, because of its canulated stem,which is inserted into the bone by using the Kirschner's guide-wire (1.8mm) to direct the screw (35° on the sagittal centerline plane and 45° onthe frontal plane anterograde), one also determines the necessary lengthof the screw. The screw is then inserted into the talus bone by theimbus spanner. The apex thread, which has the self-tightening effect,excludes the usage of the tapping device. b) so far neither of the knownoperative techniques for correction of flat feet in children—“Calcaneostop”—did not use the possibilities described in this paper.
 9. Theimplant according to the invention, according to claim 8, characterizedby the fact that it does not have a narrow part between the head and thescrew-thread, so the cortical bone does not grow over the screw, whichmakes the removal of the screw, after 3 years much easier and moresimple.